Lung biopsy tissue, obtained at cardiac surgery from patients with congenital heart defects causing elevated pulmonary venous pressure (e.g. mitral stenosis, mitral regurgitation) will be analyzed. The severity of the abnormalities in structure and growth of the peripheral pulmonary arteries will be correlated with the level of pulmonary artery pressure (Ppa) and resistance (RP) measured at the preoperative cardiac catheterization. In congenital heart defects causing increased pulmonary blood flow, the structural findings on lung biopsy tissue, previously found to correlate with the preoperative level of Ppa and Rp, will now be related to the hemodynamic data obtained at cardiac catheterization one year postoperatively. We will determine whether on the postoperative pulmonary wedge angiogram there has been improvement or worsening of the 3 features analyzed on the preoperative study, i.e. (1) rate of tapering (2) background haze and (3) pulmonary circulation time. This will be related to the severity of the structural changes seen in the lung biopsy, and to the postoperative hemodynamic outcome. The lungs from patients diagnosed as having tricuspid atresia or single ventricle will be analyzed at postmortem using injection techniques. The severity of altered structure and growth of the lung and in particular of the peripheral pulmonary vascular bed will be assessed and the factors which may have caused these abnormalities analyzed. This will, in the future identify the patients unsuited for Fontan (right atrial to pulmonary artery conduit) procedures.